The present invention relates to a sluice for feeding a material to be annealed into an annealing oven, more particularly for feeding a metallic tape which is continually fed into the internal space of the oven, wherein a buffer gas atmosphere is maintained in the oven and a sealing device should be provided before the entrance opening of the oven to protect the oven interior from ambient air.
It has been known that when metal material, for example a metal tape is to be annealed in the oven a buffer gas atmosphere should be produced in the annealing oven to prevent oxidation on the outer surface of the metal material. Such a buffer gas atmosphere can be also preferably provided at the cooling line. While the piece goods in the oven interior after the material being annealed has entered the oven, can be sealed without any problems, maintanence of a pipe buffer gas atmosphere during the transportation of the material being annealed, for example a metallic tape, still presents a problem.
Tests have shown that in order to solve the above described problems with the annealing ovens for tape-shaped metal materials a water tank has been provided in connection with the oven or the cooling line; the metal tape discharged from the oven was immersed into that tank and then after being reoriented in the water bath was transported to ambient atmosphere. Such water sealings have been, however, suitable only for flexible materials being annealed. Such water sealing can not be in practice arranged at the inlet of the oven because of an unavoidable strong steam generation in the oven interior. Steam affects the quality of the buffer gas atmosphere such that shadings or discoloration can occur on the material being annealed.
Sealing devices formed as a sluice have been known. One of them is disclosed, for example in DE-AS No. 1,149,374. Tubular elements are provided in the known device at the inlet side and the outlet side of the oven, in which tubular elements the end portions are adjusted in cross-section to that of the material being annealed. Due to the adjustment of the cross-section of each through opening in the sealing devices to the cross-section of the material being fed into the oven only small amounts of buffer or protective gas can escape from the oven. As a further means to solve the problem, a buffer gas has been fed through the oven in counter stream to the direction of transportation of the material being annealed. However, still some amounts of buffer gas escaped from the oven and too much oxygen entered the oven whereby it was impossible to completely prevent oxidation of the metal being annealed. Relatively narrow but suitable permeable sealing devices have been found specifically problematic in practice when, for example the end portions of the two metallic tapes being annealed were stitched together to avoid the interruption of operation of the oven. These superpositioned ends of two metallic tapes overlap only in a small region. If the inlet and outlet openings of the oven have a narrow cross-section adjusted to the cross-section of the single metallic tape they are too narrow to pass therethrough the tape end portions having a double tape thickness. In practice the feeding process of the metal tapes can be interrupted or the inlet and outlet openings can be dimensioned to permit passing therethrough of the overlapping portions of the tapes. However, the enlargement of these openings leads to more oxygen entering the oven interior.